People in England and Wales could be asked to declare how much they earn in the next national census, if the government approves the question.
A question on salary could be included in 2011
The Office for National Statistics is planning its first major pilot test in May 2007 - which will help shape the design for the next census in 2011.
Of the 100,000 householders taking part, half will be asked about pay.
The government is likely to decide whether a section about income and second homes is to be included in 2010.
The 2007 test will be conducted in five local authority areas, which have been selected to "reflect a range of field conditions".
They are: Liverpool, Camden, Bath and North East Somerset, Carmarthenshire and Stoke-on-Trent.
A spokesman for the Office of National Statistics said: "The census test will be voluntary.
"Information returned on the forms will be treated as confidential and only used for the evaluation of the test and carrying out any subsequent further research.
"No information that could identify individuals will be passed outside the ONS."
The Government has never before asked people to reveal their personal details about the financial situation in a census.